The probe of an NMR spectrometer serves the function of containing the sample within a uniform polarizing magnetic field, providing the means to couple the RF excitation radiation to the resonators of the sample and to couple the resonant excitation from the resonators of the sample to an RF receiver. The probe may also support sample temperature monitoring means, a turbine to spin the sample, and additional functions such as spin decoupling and field frequency lock stabilization. Dimensional constraints are imposed upon the probe because of its position within a relatively narrow gap between the poles of a magnet or within a superconductive solenoid, in order to minimize any inhomogenities of the polarizing magnetic field which would affect the precision of the resulting measurements. The external dimensional constraint is compounded by internal constraints arising from the multiplicity of probe contained apparatus.
The sensitivity of the spectrometer depends to a very large extent upon the efficient RF coupling of the reservoir coil to the resonators of the sample. In certain situations it is desirable for this coil to take the form of a saddle coil for defining and surrounding an interior volume, usually cylindrical in which the sample is housed. Saddle coils in NMR probe apparatus are discussed by Hoult, Experimental .sup.13 C Spectroscopy, Vol. III, G. C. Levy, ed., Wiley Interscience (1979). Sensitivity is related to the number of radiating resonators, e.g., the volume and density of the sample within the receiver coil of the probe. The magnitude of the sample volume is limited by the homogeneity of the polarizing field over the volume element defined by the receiver coil. For a fixed volume element it is therefore desirable to assure that the entire interior volume of the saddle coil be available for sample material.
An object of the present invention is an improved form of NMR probe coil exhibiting particular improvement in the manufacture thereof.
In one feature of the present invention, the coil comprises a pair of spiral windings, said windings of opposite helicity and symmetrically disposed about an axis, the outer portions of the respective spiral windings electrically connected in series.
In another feature of the invention the series connection between the pair of spiral windings is wholly on the surface defined by said spiral windings.
In yet another feature of the present invention, the surface defined by the spiral windings is a cylinder.
In another feature of the present invention, the spiral windings comprise printed circuit portions supported on a flexible insulating medium.
In yet another feature of the invention the flexible medium supporting the coil portions is supported in the interior of a hollow cylindrical coil form.